Dewaxing process



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DEWAXING PROCESS Filed Jan. 2o. 1940 NUYQGU 9 ...mm v un .mi Nwkww Patented Sept. 28, 1943 `DEWAXING: PROCESS l Oldrich S. Pokorny, Sarnia, Ontario, and-Herbert H. Moor, Moore Township, Lambton County, Ontario, Canada, assignors to Standard Oil Development Company, a corporation of Delaware Application January 20, 1940, Serial No. 314,784

' (c1. 19e-1s) 1 claim.

The present invention relates to the removal of waxy constituents from wax-bearing mineral oils and is especially directed to an improved process for the production of high quality petroleum waxes. In accordance with the present process, waxy constituents are removed from wax-bearing oils by chilling the oil to precipitate the waxy constituents, which constituents are then removed from the dewaxed oil by suitable means such as centrifuging, ltering, and the like. Undesirable high melting point non-waxy constituents are removed from the wax cake by heating the cake and fractionally precipitating and separating waxes of the desired melting point. l

It is well known in the art to remove waxy constituents from wax-bearing mineral oilsby various methods. In general, the waxy constituents are removed by chilling the oil to a temperature at which the waxy constituents are precipitated. The precipitated constituents are then separated from the dewaxed oil by suitable filtering or centrifuging means. In order to increase the eiciency of the dewaxing operation, various dewaxing solvents are employed. {Ihese solvents, in general, have a preferential selectivity for the non-waxy constituents and tend to throw out waxy constituents from the solution. Dewaxing solvents of this character4 are light naphtha, d

liqueed normally gaseous hydrocarbons, and the like. The cold ltrate solution comprising the dewaxed oil and the dewaxing solvent `aiter separation from the precipitated waxy constituents is handled in a manner to remove the solvent and recover the dewaxed oil. The generally y,ac- Vcepted method for the handling of the waxcake or. wax slurry in order to reduce the amount of vthe oil is to repuddle the same with additional quantities of pre-cooled solvent and then to relter the solution. The wax cake is thenhandled in a manner to remove the solvent, usually by distillation, and then subjected to various may be further refined by treatment with sulfuric acid, activated carbon or clays in order to obtain the desired color, color stability, andother characteristics. ,Y y

Y We have now discovered that indewaxing operorder of 20 F. or below. These non-waxy hydroillustrating one modification of the same. `wax-bearing mineral oil, which for the purposes means of pump -3.

' constituents. e d through mixer 5 and cooler E, in which the temperature is lowered to a point above the point of carbon constituents are characterized by a high boilingpoint in the range from about 500 F. to 550 F. at a pressure of 1 mm. of mercury, a relatively low melting point usually in the range from about 70 F. to 125 F. A. S. T. M. method, designation D 87-3'7, and a refractive index of the order of.1.433 to 1.453 at C. Since the melting points fof these non-waxy hydrocarbons are 20 F. to 50 F. below the melting points of the normal parain hydrocarbons of similar boiling po-intsvfractional distillation cannot effectively be used in order to separate these non-waxy hydrocarbon' constituents from normal highly paraiiiic waxy hydrocarbon constituents. However, we have discovered that these high molecular weight non-parafnic types of hydrocarbon constituents are more soluble in dewaxing solvents than the normal parallnic waxy type hydrocarbons. We have also discovered that the wax cake or slurry produced by liltering or centrifuging the cold waxy mixture in the d'ewaxing process cone Ytains a sufcient amount of solvent so that it is 4possible to handle thewax cake `and to Segre- -gate the non-waxy constituents from the waxy constituents by means of a fractional crystallization process.V Furthermore, it is possible, in accordance with the present process, not only to segregate 4the parainic type waxy constituents from the non-paraiiinic type non-waxy constituents, but it is also possible to segregate the paraiiinic type waxy constituents into various "relined wax fractions of varying melting points.

` The process of our invention may be readily understood by reference to the attached drawing A of description is taken to be a wax-bearing petroleum oil boiling in the lubricating oil range, is withdrawn from waxy feed oil storage I by means of pump`2 Vand mixed with a dewaxing solvent which is withdrawn from solvent storage' I8 by For purposes of `description it is assumed that the dewaxing solvent comprises methyl normal propyl ketone. The mixture( isjpassed through heater 4 in which the temperature is raised to a degree adapted to secure complete miscibility between the respective The heated mixture is passed crystallization and then divided into two streams.

One stream` is cooled under controlled condion 'the drum of lter 2e.

sired dewaxing temperature under controlled conditions in exchanger 4S and shock cooled in shock chiller 4 l The cooling medium employed may be any suitable reagent such as ammonia, al

into lteringunit lil, which for the purposes of4 description is assumed to be a rotary type filter.'

The waxy constituents accumulate as a wax'cake on the vsurface of `the drum and are removed by a scraper and delivered into ascroll' |95. removing the wax cake fromthelter drum, itis Prior'to .tions of lower melting point ranges.

temperature of which is lowered to obtain the precipitation of a wax cut having the next lower desired melting point range. The resulting precipitated wax fraction is separated from the mother liquor in a manner described with respect to the initial wax fraction precipitated. The .mother liquor is again recycledinthe manner described and the temperature progressively lowered in chiller 25 to secure additional wax frac- The mother liquor is stepwise chilled in this manner until finally a temperature is reached, at which point washed with additional wash solvent which is.

The cold substantially the entire introduced by means of spray lines Il. ltrate comprising amount of the solvent and the dewaxed oil is` Withdrawn from filter lil through filter valve [ZL and introduced into nitrate receivingrdrum I3 by-meansof line 481.-

The wash solventl introduced byv means of spray pipes Il is segregated'from the filtrate,

withdrawn through filter valve l2 and introduced into wash solvent receiver lli by means of line 49. The col-dy filtrate is passed through heat exchanger lfll and removed from the dewaxing system by means of line' 58. This. streamis then handled in a manner to completely removeI the solvent from thedewaxedi oil and to furtherV refine the d'ewaxed cillin any mannerv desirable. The cold washsoivent is. withdrawn from wash solvent receiver' lr'e by means' ofpump l 1 and line El?, passed through heat exchanger 1 and intro- :t

duced into'solvent storage I8.

The waxy constituents Yare removed from scroll te by means of pump 20, passed through heat exchanger 2l, heaterf22, and then passed into one of a series of tanks All', 0.5, 56, and lil. When v the initial tank', as for example, tank M, is filled with wax slurry, the discharge' is swung to another tank, asfor example, tank 45. The hot mixture is wit'hdrawnifrom tank 44 by means of line, 52 and pump 24, passed through Chiller 25 and introduced into filter 25, which'for the purposes of description is taken to be a rotary type filter'. The temperature of the mixture leaving chiller 25A and passed to filter. Zis controlled to precipitate the' particular wax fraction desired. The precipitated wax is removed and segregated The segregated wax is washed completely free of mother liquor by means of fresh solvent which is withdrawn from solvent storage 23 by means of line 53 and pump 34, passed through heat exchanger 2 l, further chilled in Chiller 35,- and then introduced into lter 2t by means oi spray-lines 2l. Any suitable refrigerant may be employed inchiller. 35, as for example, ammonia, a liquee-d normally gaseous` hydrocarbon such as propanez or thelike.

The precipitated wax is removedfrom the drum oflter 2S, delivered intoscroll 28, and removed from the system vby means of pump 29 and line 54. sirable manner by treatment with sulfuric acid, clays, and the. like. The mother liquor combined with'the wash solvent is. removed from lter 25 by means of line 55, passed into wash solvent drum 30 and thendelivered by means of pump,

il to one of' the emptyv tanks, as for example, tank 45. When tank Ml, is empty and tank 4S is full, the valves are adjusted so that the liquor is removedffro-.rn tank L55. The mixture removed from tank deis passed. through chiller 25, the

The wax may be further rened in any de-` kmalpropyl ketone.

yoperation described above.

the mother liquor removed from lter 25 by v means of' line 55 contains nothing but dissolved ered to the spray lines of filter lll as described above. The mother liquor free of waxy constituents may also be delivered to exchanger I and utilized for diluting the incoming waxy feed oilfassdescribed. Ii spent mother liquondelivered byv means of pumplis` insulcierrt for thewash requirements in iilter Hl; fresh chilledr solvent from; Chiller-3e may. also be employed as wash solvent.. It is: to be understood' that by means of bypass 3l fresh solvent may be used for diluting the incoming waxy feed; f

The pro-cess of the present invention may be widely varied. The operation may be employed for the removal of waxy constituents and for the production of. desirable waxfractions from any feedoil. rIThe waxy constituentsmay be preci-pn itated in any desirable manner. Indirect chilling of the waxy feed oil may be secured by the use of ammonia or by means of an equivalent solvent. The waxy charge oil may be directly chilled by utilizing a refrigerant of the type ofA ay liqueed normally` gaseous hydrocarbon, asior. example,

propane.

Although the present process may be employed inany-dewaxing operation, it is particularly apkdesired that the alkyl group contain at leas three carbon atoms. Typical examplesiof this groupA of solvents are methyl normal propyl 11etone, methyl normal butyl ketone, and ethyl nor- An especially preferred solvent is a mixture of methyl normal propyl ketone with methyl normal butyl ketone. These solvents are characterized by extremely low wax solubility at dewaxing temperatures, by low miscibility temperatures with oil and by extremely high filter rates in solution with the oil at low temperatures.` The structure of the wax cake formed in the dewaxing operation is ,such that the oil content of the slack wax can be reduced down tobetween 3% and 15% by means of the washing We have 4discovered that when using solvents of this character, a

carbon constituents of wax-bearing lubricating oil distillates by means of fractional crystallization. Because of the high selective action upon normal paran waxy hydrocarbons and the low oil content of the lter cake, our process also permits fractionation of waxes according to their melting points. Although it is preferred that the wax cake be heated and handled in the manner described without the addition` of additional solvent, under certain operating conditions it may be desirable to add additional solvent to the wax slurry produced in the solvent dewaxing operation in order to improve the deoiling of the solid waxy hydrocarbon constituents which separate out during the respective cooling stages.

In order to further illustrate our invention, the following examples are given which should not be construed as limiting the same in any manner whatsoever:

EXAMPLE 1 A Mid-Continent crude waxy distillate boiling in the lubricating oil range having a viscosity of 75 seconds Saybolt Universal was dewaxed as described using methyl normal butyl ketone as the dewaxing solvent. The wax cake, secured had a Saybolt viscosity of 48.5 seconds at 210 F. and contained between about 17% to 25% of solvent-free slack wax. The wax cake was heated to ya temperature above about 100 F. in order to completely dissolve all the hydrocarbons in the dewaxing solvent remaining in the filter cake after the solvent dewaxing step. The solution was then cooled in the manne;1 described to a temperature of about 105 F., 90 F., 80 F., 65 F., 40 F. and 0 F. After each chilling stepgc'he crystalline solids were separated from the mother liquor by means of a filter. The respective wax cakes were washed with relatively small amounts of wash solvent and the respective resulting ltrates mixed with the mother liquor. The respective wax cakes were completely freed of solvent by means of a distillation step. The mother liquor filtrate from the nal separation step co-nducted at a temperature between about +25 F. and F. contained substantially all the oil originally present in the wax cake, as well as from to 30% of very low melting point range nonparaflinic type hydrocarbon constituents. The

pour point of this oil varied between about 30 F. and 45 F. Since a concentration of oil in this mixture of mother liquor and wash solvent resulting from the respective deoiling and recrystallization stages is in the range from about 2% to 5%, it is not necessary to remove the solvent in order to recover the dissolved oil. It is more advantageous to add the solvent mixture with the feed waxy distillate or toV employ the mixture for washing the wax cake formed in the filter. Thus, the oil is ultimately disposed in the original ltrate at the dewaxing plant as dewaxed oil.

The results of the operations were as follows:

Table 1 Charge of wax lter cake. 2315 pts. by Temp. of filtration and washlng, F 113 105 Volume of wash solvent used, pts. 500 310 Yield of wax (solvent-free) pts. by wt 26. 9 30.1 Melting point, A. S. T. M., F 163.0 158.0 Expressible oil, per cent by wt. N

Type of solid hydrocarbons.

Refractive index at- S0 C D 80 C dewaxing plant wt. containing` 410 pts. slack wax when dewaxing parain distillate having a Saybolt Universal viscosity of 168 seconds at 100 F. to +10 F. pour point was heated to about 130 F. to effect substantially complete solution of the solid constituents. The solution was cooled in a number of steps as described to a temperature of about F., '75 F., 64 F., 40 F. and +8 F. After each cooling step the precipitated wax was segregated by filtration or centrifuging. The wax cakes so formed were washed with relatively small amounts of fresh dewaxing solvent and the solvent recovered from the respective wax cakes by distillation or other means. The' yields of waxes obtained are summarized below:

Table 2' Charge of wax slurry (filter cake) 2950 pts. by wt., containing 534.5 pts.

by wt. of slack wax Temp of filtration and wash- The process of the present invention is not to be limited by any theory or mode of operation, but only in and by the following claim in which it is desired to claim all novelty in so far as the prior art permits'.

We claim: Y n Improved process for the removal of waxy constituents from waxy petroleum oils and for the segregation of said waxy constituents into various melting point fractions substantially free of non-waxy hydrocarbons having relatively low melting points, comprising mixing with said waxy petroleum oil a solvent selected from the class of aliphatic ketones characterized by containing an alkyl group and a total of ve or six carbon atoms in the molecule, heating said mixture to secure complete miscibility between the respective constituents, chilling the heated mixture to a temperature at which said waxy constituents precipitate, separating a filtrate comprising the dewaxed oil and dewaxing solvent, removing the dewaxing solvent from said dewa-Xed oil, separating the waxy constituents, reheating the same to a temperature at which a liquid miscible phase is secured, gradually cooling the heated liquid under conditions adapted to progressively fractonally crystallize oil-free wax fractions of progressively lower melting point ranges substantially free of non-waxy low melting point hydrocarbons and under conditions adapted to retain the low melting point nonwaxyconstituents in the mother liquor, separating the respective wax fractions as they crystallize, washing the respective wax fractions with fresh solvent, combining the mother liquor and the respective wash ltrates and returning the mixture to the waxy feed oil.

l Nil Nil 88 0. 53 nhydrocarbons Solid hydrocarbon constituents of an unknown structure.

OLDRICH S. POKORNY. HERBERT H. MOOR. 

